RPIC

Medical Isotopes

One of the recommendations of the UDP was for the Saskatchewan government to support a research reactor at the University of Saskatchewan. The UDP noted that sales of isotopes would not cover the costs of the reactor. The "crisis" resulting from the Chalk River NRU shut-down for safety reasons led to an intense debate about medical isotopes and Canada's supply. It turns out that many procedures do not require isotopes from a nuclear reactor, and that most uses of nuclear medicine are for diagnosic purposes - not for treatment. Nuclear proponents appear to be cynically using the general public's lack of technical knowledge and their concern for other people's health as a lever to gain acceptance of a reactor that would primarily be use for commercial research, likely to promote tar sands development.

The nuclear industry promotes nuclear power and medical uses of radionuclides
as inextricably linked. In 1991, when Bill C-204 (placing a moratorium on
further nuclear power plants in Canada)
was introduced in parliament, the industry went into full propaganda mode, even
claiming that x-ray machines would be affected!(Well, perhaps not“claiming” but not denying the rumour
either.)

Radioisotopes entered medical use before nuclear reactors. At first, naturally
occurring radium-226 and radium-224 were used. In the 1940's, use of a
cyclotron for bombarding various target materials created new radioisotopes.
From their discovery, physicians were fascinated by these substances that could
destroy cells with or without direct contact. Strontium-90 was used as a salt
to destroy superficial skin cancers. The early brachytherapy* beads contained
radium-226, iridium-192 or palladium-103. Their use has always required a
cautious approach, finding a dose that cured with a minimum of side effects.
There is no doubt that current radioisotopes are useful for both diagnostic and
treatment purposes.

Some of the radioisotopes in current use:

1. Cobalt-60 is produced in some nuclear power
reactors. It is a gamma emitter and used to sterilize medical instruments
and as an external treatment of some solid cancers.

2. Technetium-99m is produced through the decay of
Molybdenum-99 which, in turn, is produced in nuclear reactors designed for
isotope production (not nuclear power). Tc-99m is used in imaging to make
diagnoses. Tc-99m is a gamma emitter but has such a short half life that it
poses next to no problem in terms of waste; its short-lived activity means that
the patient is exposed to a low dose of gamma rays. When its availability was
limited last year, physicians discovered that judicious use of PET scans and
ultrasound could serve much the same purpose.

3. Gallium-67 is cyclotron-produced by the proton
irradiation of enriched zinc oxide. It is a gamma-emitter with a half-life of
78.3 hours. For cancer staging, gallium scans have largely been replaced by PET
scans, or positron emission tomography. Gallium-67 continues to be useful
in the imaging of inflammation and infection.

4. Cesium-131 is probably the “new” radionuclide for
brachytherapy, the insertion of radioactive beads into the cancerous growth. It
is produced by radioactive decay from a neutron-irradiated naturally occurring
barium-130 or from enriched barium containing barium-131. The source of the
neutrons can be a nuclear reactor or another neutron generating device such as
a linear accelerator or neutron generator.

5. Iodine-131 is a fission product of uranium in nuclear
reactors or of plutonium in nuclear bombs. Its principle use is for ablation of
thyroid cancer cells but it is also used in brachytherapy.

Radionuclides and nuclear power?

1. New reactors are not required to keep medical sources supplied. We
will have enough for many years with our current reactors.

2. Research indicates that molybdenum-99, the radioisotope whose shortage
caused havoc last winter, can be produced by using a cyclotron with a
molybdenum-100 target.

3. The use of cobalt-60 may be phased out altogether, as safer alternative
technologies take over -- especially since several patients have been injured
by cobalt-60 radiotherapy devices due to programming errors in the computerized
AECL radiotherapy units; alternative radioisotopes may be found which can be
produced in cyclotrons and which can substitute for cobalt-60, or a method may
be developed for producing cobalt-60 economically in an accelerator.

4. Arrangements may be made to maintain a number of small reactors in
operation solely for the purpose of producing selected radionuclides for use in
medicine , industry and scientific research.

I personally believe that in a number of years, we will look back on
radioisotope diagnosis and treatment like our modern perspective on
blood-letting or, more recently, open-abdominal surgery for gall bladders and
uteri, beneficial when we didn't know how to do anything else but "out of
date" because it will have been replaced with better, less risky
treatment.

==

* Brachytherapy: a form of radiotherapy where a radioactive source is
placed inside or next to the area requiring treatment.